The origin of Neotropical diversity has intrigued scientists since Humboldt and Wallace. Species radiations in this region have been associated with major biogeographic events such as Quaternary climatic changes (1), Neogene geological changes such as the Andean uplift, closure of the Panamanian isthmus, Miocene Marine incursions, and the formation of the Amazon river basin (2). Less attention has been devoted to the importance of regional biotic interchange in shaping extant Neotropical diversity patterns. In PNAS, Antonelli et al. (3) marshal an impressive array of species occurrence and phylogenetic data from six major clades (i.e., angiosperms, ferns, squamates, birds, mammals, and frogs) to test the amount of immigration among Neotropical regions. This study finds that Amazonia is by far the greatest contributor of lineages to other regions, which has direct implications for our current understanding of the processes that underlie the origin and maintenance of diversity in the world’s most species-rich region. These results shed light on the biogeographic connections among Neotropical regions over time and identify which regions have experienced the most interchange and which have been more isolated.

Many new phylogenetic studies have contributed to our understanding of global diversity patterns and, in general, have provided support for the “Out of the Tropics” (4) and “Tropical Conservatism” (5) hypotheses, with older tropical clades giving rise to younger temperate lineages (6, 7). Tropical wet forest biomes are well known as the source of global biodiversity, due to their large time-integrated area, high productivity, more intense biotic interactions, and relatively stable climate (8). These factors promote large cumulative average population sizes, which, in turn, promote speciation while decreasing the risk of extinction (8). However, very few studies have looked at the patterns of diversity and dispersal among tropical regions. The factors that influence speciation and extinction of resident lineages may …

↵1To whom correspondence may be addressed. Email: paulfine{at}berkeley.edu or llohmann{at}usp.br.

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